DE60025355T2 - STRAIN GAUGES - Google Patents

Description

TECHNICAL TERRITORY

The The invention relates to an example in a pressure sensor or a load cell to be used.

STATE OF TECHNOLOGY

Became conventional a thin film strain gauge at a Automobile pressure sensor, a pressure sensor for measuring pressure or a load, a load cell and the like used.

More accurate is a thin film strain gauge on one directly on the metal diaphragm of a pressure sensor or the support element formed insulating layer provided a load cell, and is used for pressure measurement, etc.

A case where a strain gauge is used in a pressure sensor will be described below with reference to FIGS 3 and 4 described.

3 shows a schematic view showing a main portion of a pressure sensor and 4 shows a diagram of the in 3 shown pressure sensor.

If according to 3 a strain gauge is used in a pressure sensor, one of four gauge layers ( 12 . 13 . 14 and 15 ) existing Meßmustermuster example on a metal diaphragm 5 formed by the intermediate storage of an insulating layer by a photolithography process or the like.

4 also shows a schematic of the pattern.

Due to the structure described above, any change in the pressure (strain) on the diaphragm will result 5 to a corresponding deformation of the diaphragm 5 ,

Thus, deformation of the diaphragm results 5 to a change in the bracing portions in the respective on the diaphragm 5 trained meter layers 12 . 13 . 14 and 15 ,

According to 3 varies the strain coefficient on the diaphragm 5 according to the position, so that the bracing portions of the respective Meßinstrumentschichten 12 . 13 . 14 and 15 are not the same. When the bracing portions of the respective meter layers 12 . 13 . 14 and 15 thus changed in response to a change in pressure, the electrical resistances of the respective Meßinstrumentschichten 12 . 13 . 14 and 15 also changed.

Thus, the change in 4 shown resistance values R ₁ , R ₂ , R ₃ and R ₄ according to the pressure, so that the output voltage V1 is changed with respect to the input voltage V0. Since the output voltage V1 is linearly changed according to the pressure change, it is possible to measure the pressure from the output voltage V1.

The However, the known techniques described above bring the problems listed below with himself.

The for the Material for the meter layer required main features to Achieving an improvement in performance and properties of such a pressure sensor or the like are as follows: (1) small temperature coefficient of resistance (below with TCR), (2) a high strain sensitivity (K-factor), (3) a high resistivity, (4) a slight change resistance with time, (5) independence of strain sensitivity from the temperature etc.

In view of this, a metal strain gauge made of, for example, NiCr has been put to practical use. However, as a result of the improvement in the various performances of vehicles and other devices using the pressure sensor or the like, the demand for improvement in the performance and the characteristics of various has increased NEN parts and sensors, and for the materials used in the prior art, it is difficult to meet this demand.

If For example, a silicon semiconductor for the meter material is used, which has a high strain sensitivity of about several Having ten, this shows a high sensitivity to a Pressure change, and thus proves to be effective material. His TCR is however pretty big, and his linearity is inadequate, so it for a precise measurement needed is to provide a special device for temperature compensation.

For a use as a meter material has, for example, an alloy NiCr type or CuNi type alloy metal material a low TCR (several to several hundreds ppm / K). on the other hand it has a low strain sensitivity of about 2, resulting in a low sensitivity to a pressure change leads.

When Instrument material with a high strain sensitivity was a chromium material (with a strain sensitivity of about 10) was examined. Due to its poor output temperature characteristic (TCR, etc.), however, it has not yet been put to practical use.

On This way is used when choosing a material with a low TCR included a low strain sensitivity. on the other hand refers to the selection of a material with a high strain sensitivity a big TCR with one. Thus, it was impossible in the prior art, at the same time a high strain sensitivity and a small TCR.

From From this point of view, a metal thin film strain gauge has also been proposed, wherein a Fe-Cr-Al alloy thin-film resistor by evaporation, Atomize or The like is formed into a layer as the resistance of a metal thin-film meter is (see for example the document JP-A-137804 (1994)).

Even with this strain gauge However, the strain sensitivity was still rather low. Consequently there was a demand for a tension measuring device with a high strain sensitivity and a reduced temperature coefficient of resistance.

In addition, the document discloses US 4,462,218 a semiconductor strain gauge with integrated compensation resistors, wherein on a base material, such as a substrate, different layers are arranged for obtaining integrated temperature compensation by providing different materials with different temperature coefficients of resistance (TCR). Therefore, platinum alloy gauge resistors are placed on a silicon dioxide layer to form a resistance bridge circuit configuration. The materials having a negative or positive thermal coefficient of resistance provide partial compensation of the temperature dependence of the resistances of the strain gauge for a reduced temperature dependence and a sufficiently high strain sensitivity.

The publication US 5,549,006 discloses a pressure transducer employing different layers of semiconductor materials having a first conductivity type exhibiting a negative temperature coefficient of resistance, and having a second conductivity type opposite to the first conductivity type and exhibiting a positive temperature coefficient of resistance. The sensors are electrically connected to form a resistance bridge for evaluating their output signals. The different temperature coefficients of the resistor provide compensation for the temperature dependence of the pressure transducer. Temperature dependence is greatly suppressed for obtaining increased accuracy of pressure measurement.

The publication US 3,753,270 discloses a strain-sensitive semiconductor element having a predetermined temperature coefficient of resistance wherein different temperature coefficients of resistance are provided by doping impurities in a semiconductor crystal wafer. Different regions of the same conduction type but with different temperature coefficients of resistance are obtained. The proportionate volumes of the regions are varied by adjusting the relative volumes of the many regions for obtaining specific desired temperature coefficients of resistance.

Finally, the document discloses US 5,508,676 a strain gauge on a flexible Support, wherein the measuring instrument comprises a thin layer which is sensitive to deformation, and which is etched in resistance and fixed on a flexible support. The thin film has at least two underlying layers with different creep values with respect to the deformation. A first underlying layer, which is preferably formed of an alloy, has a positive creep value, whereas a second underlying layer has a negative creep value. A compensation of the temperature coefficient for the resistance is obtained.

The Invention was for solution the above problem in the prior art. It's up to you underlying, a strain gauge with a high strain sensitivity and a reduced temperature coefficient of resistance (TCR) to provide an improvement in terms of capacity to achieve.

According to the invention this Problem solved by a stress measuring device according to the appended claims.

The comprises tension measuring device according to the invention in particular a layered structure, one of a positive TCR material formed first layer and one of a negative TCR material formed second layer includes. The first and enclose second layer sandwiched an intermediate layer. The first layer is one Material formed whose temperature coefficient of resistance is positive, and the second layer is formed of a material whose temperature coefficient of resistance is negative, and the Interlayer is to avoid mutual diffusion of the respective materials of the first and second layers.

Even if to increase the strain sensitivity of the tension measuring device as a whole materials with a high strain sensitivity than Materials for forming the first and second layers are selected is it thus possible the temperature coefficient of the resistance of the tension measuring device as Whole to reduce, because the materials have a positive or negative Have temperature coefficient of resistance. It also provides due to the layered structure, each layer has an interface effect ready to thereby further increase the strain sensitivity. The The first layer is preferably made of a crystalline metal material formed, and the second layer is preferably made of an amorphous Material formed. The second layer is preferably tantalum educated.

SUMMARY THE DRAWING

1 shows a schematic sectional view of a strain gauge according to an embodiment of the invention (with a two-layer structure);

2 shows a sectional view of a strain gauge according to an embodiment of the invention (with a three-layer structure);

3 shows a descriptive view of a main portion of a pressure sensor; and

4 shows a diagram of the in 3 shown pressure sensor.

BEST EMBODIMENT TO EXECUTE THE INVENTION

preferred embodiments and examples of the invention are exemplified below Reference to the drawing closer described. It should be noted that the dimensions, materials, Configurations, positional relations, etc. in the embodiments and examples of specified ingredients are not as specified in the appended claims Restricting scope of invention to be understood.

In addition, the strain gauge according to the embodiment of the invention is applicable to various well-known sensors or the like, except as described above in connection with the prior art with reference to FIGS 3 and 4 described pressure sensor. However, since such sensors are well known in the art, their description is omitted.

Tension measuring devices according to the embodiments of the invention are described below with reference to FIGS 1 and 2 described.

The 1 and 2 show sectional views of strain gauges according to examples and embodiments of the invention. 1 shows a two-layer structure and 2 shows a three-layer structure.

At first this is in 1 described tension measuring device described.

According to the drawing is a strain gauge 10 on a substrate 2 formed and between a pair of electrodes 3 and 4 arranged.

The tension measuring device 10 has a layered structure composed of a first layer formed of a positive TCR material 10a and a second layer formed of a material having a negative TCR 10b composed.

These layered structure provides an interface effect between the respective Layers ready, causing an increase in strain sensitivity can be expected.

Further in the present example, material with positive TCR and a material stacked together with negative TCR, leaving itself if a material with a high strain sensitivity for each layer selected it becomes possible is to reduce the TCR of the strain gauge as a whole.

That is, when a material having a high elongation sensitivity than the material for the first layer 10a is selected is the TCR of the first layer 10a positive and big.

Thereby, a material having a reasonable strain sensitivity whose TCR is negative and large becomes the material for the second layer 10b selected.

By combining and stacking the first layer 10a and the second layer 10b it is possible to use the TCR of the tension measuring device 10 to reduce as a whole.

Thus, the tension measuring device allows 10 as a whole, a reduction in the TCR, while the strain sensitivity is increased, and is superior in terms of sensitivity and temperature dependence. Therefore, when applied to various sensors or the like, it enables an improvement in the performance of such sensors and the like to be achieved.

wobei R1 und R2 die jeweiligen elektrischen Widerstände der ersten Schicht 10a und der zweiten Schicht 10b zwischen den Elektroden 3 und 4 bei einer Temperatur T bezeichnen; R1' und R2' die jeweiligen Widerstände der ersten Schicht 10a und der zweiten Schicht 10b zwischen den Elektroden 3 und 4 bei einer Temperatur T' bezeichnen; ΔT die Temperaturdifferenz (ΔT = T – T') bezeichnet; α = R1'/Rl ist; und β = R2'/R2 ist.Furthermore, let the respective temperature coefficients of the resistance of the first layer 10a and the second layer 10b according to 1 designated TCR 1 and TCR 2. Assuming that the first layer 10a and the second layer 10b connected in parallel, the TCR of the tension measuring device 10 as a whole are expressed by Equation 1 given below:

where R1 and R2 are the respective electrical resistances of the first layer 10a and the second layer 10b between the electrodes 3 and 4 at a temperature T; R1 'and R2' are the respective resistances of the first layer 10a and the second layer 10b between the electrodes 3 and 4 at a temperature T '; ΔT denotes the temperature difference (ΔT = T - T '); α = R1 '/ R1; and β = R2 '/ R2.

If suitable materials selected become possible this equation controls the TCR value.

(Embodiments)

Below is the in 2 described tension measuring device described.

While that in 1 has shown a two-layer structure shown in FIG 2 shown strain gauge 11 a three-layer structure.

The tension measuring device 11 is composed of a first layer formed of a material having a positive TCR 11a and a second formed of a material having a negative TCR layer 11b and an intermediate layer 11c together.

More precise is this strain gauge 11 constructed so that it compared to that described in the above 1 shown bracing the intermediate layer 11c having. Incidentally, the structure is the same, so the description thereof is omitted.

The intermediate layer 11c is provided to allow for mutual diffusion of the constituents of the respective materials of the first layer 11a and the second layer 11b to avoid, which may occur depending on the materials for the layers, for example, in the formation of the first and the second layer. The intermediate layer is preferably formed of tungsten, for example.

The structure described above may also have the same effect as that in FIG 1 provide shown.

wobei R3 den elektrischen Widerstand der Zwischenschicht 11c zwischen den Elektroden 3 und 4 bei der Temperatur T bezeichnet; R3' den elektrischen Widerstand der Zwischenschicht zwischen den Elektroden 3 und 4 bei der Temperatur T' bezeichnet; und γ = R3'/R3 ist. Die anderen Symbole bezüglich der ersten Schicht 11a und der zweiten Schicht sind dieselben wie die bei Gleichung 1 verwendeten.The temperature coefficient of resistance of the material for the intermediate layer 11c be designated TCR 3. The TCR of the tension measuring device 11 as a whole, it can be expressed by Equation 2 given below:

where R3 is the electrical resistance of the intermediate layer 11c between the electrodes 3 and 4 denoted at the temperature T; R3 'the electrical resistance of the intermediate layer between the electrodes 3 and 4 at temperature T '; and γ = R3 '/ R3. The other symbols related to the first layer 11a and the second layer are the same as those used in Equation 1.

If suitable materials selected become possible this equation controls the TCR value.

While at the above description layered structures with two or three layers are used as examples, it is noted that the same effect also by applying an appropriate multilayer structure can be obtained with multiple layers.

Examples for the Positive TCR materials include a general crystalline one Metal (chromium (Cr)), and examples of the material with negative TCRs include an amorphous metal (eg, ZrCu).

specific Examples in which suitable materials according to the preceding embodiments selected are described below.

(Example 1)

The following describes the case where a material for the first layer formed of a positive TCR material is Cr (Cr) in which the material for the second layer formed of a negative TCR material is an alloy of zirconium and copper (Zr ₆₁ Cu ₃₉ (atomic%), hereinafter referred to as ZrCu), which forms an amorphous alloy, and in which the material for the intermediate layer used as a diffusion barrier material 11c Tungsten (W) is a positive TCR material.

At first were thin layers of ZrCu, W and Cr in this order on a glass substrate a sputtering process educated.

After that an Au / W electrode was formed by a sputtering process, and a heat treatment was at 300 ° C for four Hours in atmospheric Environment executed.

there the thickness of the ZrCu layer was 300 nm, that of the W layer was 25 nm, and that of the Zr layer is 10 nm.

Of the TCR and the strain sensitivity of the thus formed layered Position (of the tension measuring device) were measured.

The TCR was calculated from resistance measurement results obtained by a digital multimeter in the Range of -45 ° to 131 ° C were obtained, and the strain sensitivity was obtained from the rate of change in the resistance when a strain was applied by a four-point bend.

moreover were compared for the respective TCR and strain sensitivities of the constituent materials of the layered layer.

Further, for comparison, the TCR and the elongation sensitivity of a structure obtained by forming a thin film (having a film thickness of 300 nm) of Ni ₇₈ Cr ₂₂ (atomic%) (= Ni ₈₀ Cr ₂₀ (% by weight)) on a glass substrate by a sputtering process also measured.

table 1 shows the measurement results.

Tabelle 1

Table 1

The Symbol G denotes the glass substrate.

As from Table 1, it was possible to increase the strain sensitivity to increase and reduce the temperature coefficient of resistance (TCR), what about achieving an improvement in performance allowed.

(Example 2)

below the case is described in which the material of a positive TCR formed first layer of a multi-layer layer Chromium (Cr) and tungsten (W) consists, and in which the one of a material formed with negative TCR second layer of tantalum (Ta) consists.

At first was a multi-layer layer of alternately stacked Cr and W layers (at the five Cr layers and four W layers alternately stacked to form the first layer are formed on a glass substrate by a sputtering process. After that, a Ta thin film was formed formed thereon with a thickness of 154 nm.

Under Using Equation 1 for obtaining the TCR, the thickness of each layer was adjusted that the TCR is about 40 ppm / K.

After that an Au / W electrode was formed by a sputtering process, and a heat treatment was in atmospheric Environment at 300 ° C for four Hours running.

Of the TCR and the strain sensitivity of the thus formed layered Position (of the tension measuring device) were measured.

The Measuring method and the like were the same as in Example 1. Further, as in Example 1 the respective TCR and strain sensitivities of the constituent materials the layered layers also measured.

table 2 shows the measurement results.

Tabelle 2

Table 2

The Symbol G denotes the glass substrate.

As from Table 2 was an increase in strain sensitivity and a reduction in the temperature coefficient of resistance (TCR) possible, with an improvement regarding the efficiency was achieved.

According to the above Description according to the invention has a stress measuring a layered Structure on, the one made of a material with a positive TCR trained layer and one made of a material with a negative TCR formed second layer, thereby increasing the Strain sensitivity and a reduction of the temperature coefficient the resistance is possible and thus an improvement in performance is achieved.

The The first layer is preferably made of a crystalline metal material formed, and the second layer is preferably made of an amorphous Metal or tantalum formed.

COMMERCIAL APPLICABILITY

According to the above Description is the strain gauge according to the invention for use in an automotive pressure sensor, a pressure sensor for measuring Pressure and load, a load cell, etc. suitable.

Claims (5)

Tension measuring device ( 11 ) having a layered structure with a first layer ( 11a ), a second layer ( 11b ) and an intermediate layer ( 11c ) sandwiched by the first layer and the second layer, characterized in that the first layer is formed of a material whose temperature coefficient of resistance is positive, the second layer is formed of a material whose temperature coefficient of resistance is negative , and the intermediate layer is provided for facilitating mutual diffusion of the constituents of the respective materials of the first layer ( 11a ) and the second layer ( 11b ) to avoid. A tension measuring device according to claim 1, wherein the first layer formed of a crystalline metal material is. Tension measuring device ( 11 ) having a layered structure with a first layer and a second layer, characterized in that the first layer is formed of a multi-layer consisting of chromium and tungsten, and the second layer ( 11b ) is formed of a material whose temperature coefficient of resistance is negative. Stress measuring device according to claim 1, 2 or 3, wherein the second layer is formed of an amorphous metal. Stress measuring device according to claim 1, 2 or 3, wherein the second layer is formed of tantalum.